Since You're in UK, I'll tell you a failure I had with certain spiro's.
I used to take spiro by a brand I forgot name, but the packaging was white with orange stripes, some time ago they gave me a different one, the packaging was blue red and white, the brand is actavis, and the dosage was the same, yet the new one must have been a bad batch since my tst went from 0.6 to 37.5!!
DEFINITELY check your tst